I've clicked on OK and got the standard Google screen and clicked on their Allow button, but that doesn't seem to work in the last case I tried this morning, i.e the Re-authenticate button on the Account tab doesn't grey out.

Why is this message coming up on only a few of our many Syncdocs clients? Has Google changed their security just recently?

I've done the alternative procedure Google offer, where you get two URL's and eventually paste in the Google token, on two other customers and it worked, but I was not offered the other way today ...

Help! If this is going to happen on all our current users of Syncdocs, I am in for a load of work!

Is it possible to email us a copy of the Syncdocs log file from one of the machines, and if possible some screen shots of the greyed out button. This might show us more details of the Google error, and will also show us the error code we can use to contact Google Support.

You can get the log file by right clicking on the Syncdocs icon, selecting "Preferences", then "Advanced" and then "View Log".
(if you do not see an "Advanced" tab, click on "Advanced options..." button to see it). Our email address is contact-syncdocs@syncdocs.com